docs: def contraction_sharp(Di1, Di2):
      r'''Returns loss coefficient for any sharp edged pipe contraction
      as shown in [1]_.
  
      .. math::
          K = 0.0696(1-\beta^5)\lambda^2 + (\lambda-1)^2
  
      .. math::
          \lambda = 1 + 0.622(1-0.215\beta^2 -  0.785\beta^5) 
  
      .. math::
          \beta = d_2/d_1
  
      .. figure:: fittings/contraction_sharp.png
         :scale: 40 %
         :alt: Sharp contraction; after [1]_
  
      Parameters
      ----------
      Di1 : float
          Inside diameter of original pipe, [m]
      Di2 : float
          Inside diameter of following pipe, [m]
  
      Returns
      -------
      K : float
          Loss coefficient in terms of the following pipe [-]
  
      Notes
      -----
      A value of 0.506 or simply 0.5 is often used.
  
      Examples
      --------
      >>> contraction_sharp(Di1=1, Di2=0.4)
      0.5301269161591805
  
      References
      ----------
      .. [1] Rennels, Donald C., and Hobart M. Hudson. Pipe Flow: A Practical
         and Comprehensive Guide. 1st edition. Hoboken, N.J: Wiley, 2012.
      '''
      beta = Di2/Di1
      lbd = 1 + 0.622*(1-0.215*beta**2 - 0.785*beta**5)
      return 0.0696*(1-beta**5)*lbd**2 + (lbd-1)**2